Re: [Qemu-devel] [PATCH v11 14/15] rdma: introduce MIG_STATE_NONE and change MIG_STATE_SETUP state transition

[Paolo Bonzini]

Il 25/06/2013 22:56, Michael R. Hines ha scritto:
>>
> I was wrong - this does require a protocol extension.
> 
> This is because the RDMA transfers are asynchronous, and thus
> we cannot know in advance that it is safe to unregister the memory
> associated with each individual transfer before the transfer actually
> completes.
> 
> While the destination currently uses the protocol to participate in
> *registering* the page, the destination does not participate in the
> RDMA transfers themselves, only the source does, and thus would
> require a new exchange of messages to block and instruct the
> destination to unpin the memory.

Yes, that's what I recalled too (really what mst told me :)).  Does it
need to be blocking though?  As long as the pinning is blocking, and
messages are processed in order, the source can proceed immediately
after sending an unpin message.  This assumes of course that the chunk
is not being transmitted, and I am not sure how easy the source can
determine that.

Paolo